The present invention relates to turbine shrouds, and more particularly, to a metal-ceramic turbine shroud.
Turbine shrouds of all-metal construction have been widely employed. However, the effective life of such all-metal turbine shrouds is limited due to excessive oxidation and erosion caused by exposure to the high velocity hot gas stream in a turbine engine. As a result of this shroud material loss, clearances increase between rotor blade tips and the now-receding shroud. These increased clearances cause performance degradation due to lower efficiency. In addition, these increased clearances reduce the life of hot parts in the engine due to the higher gas temperatures needed to deliver constant thrust and also due to temperature overshoots.
It would appear that ceramic materials would offer potential advantages over metals in such hot shroud applications due to the superior oxidation and erosion resistance of ceramic materials with respect to metals. However, attempts to utilize ceramics have encountered severe problems. Such problems include: attachment stresses in the brittle ceramics; conduction of excessive heat through the ceramic; fabrication problems, e.g., high cost, low yield, due to the ceramics' extreme hardness and tendency to crack or chip; and material flaws that are very difficult to inspect.
It is, therefore, an object of the present invention to provide an improved turbine shroud structure.
Another object of the present invention is to provide such a turbine shroud structure which is a composite metal-ceramic structure providing desirable structural features of metal shrouds with desirable environmental resistance features of ceramics.